In pumps of the type mounted on fire trucks for fire fighting service there is a need for a transmission for the pump capable of operating with the high torques put out by the transmissions of the newer fire trucks.
One type of pump transmission in use today comprises an input flange keyed onto an input shaft, an output flange keyed onto an output shaft, and a sliding gear which slides between a "ROAD" position and a "PUMP" position. The input flange is connected to the transmission on the fire truck to be driven thereby and to cause rotation of the input shaft keyed thereto. The output flange is connected to the rear wheels of the fire truck for driving the same. The sliding gear is slidable axially on a splined portion on the input shaft. In the "ROAD" position of the sliding gear, its gear teeth are engaged with internally facing gear teeth formed in a collar that is part of the output shaft. In this manner, torque is transmitted from the input shaft to the output shaft which has its output flange connected to the rear wheels of the fire truck for driving same. In the "PUMP" position of the sliding gear, its teeth are engaged with the driving gear of the pump which is mounted adjacent to the pump transmission.
While the above-described conventional pump transmission is satisfactory for the torque loads of transmissions of the older fire trucks, it would be impractical to construct such a unit to withstand the much higher torques of the newer transmissions.
It is the general object of the invention to provide a compact pump transmission of the indicated type which is very strong so that it can operate with very high torque truck transmissions and, at the same time, is less expensive to manufacture than a comparable prior pump transmission design.
Briefly stated, the greater strength of the pump transmission in accordance with the invention is achieved by constructing the transmission of an input member having a splined shaft portion and an input flange portion, an output member having a splined shaft portion and an output flange portion, the splined portions of the input and output shaft being axially aligned and of the same configuration, and a sliding gear having an internal splined portion adapted to slide along the splined portions of the input and output shaft portions. The unit is constructed so that in the "ROAD" position, the sliding gear is engaged with both the splined portions of the input and output members. In the "PUMP" position the sliding gear is engaged with the splined portion of the input member only and has its gear teeth engaged with a driving gear of the pump.
The design in accordance with the invention involving the two splines on the input and output shaft portions is double the strength of the arrangement of the prior art using a collar with internally facing gear teeth. Moreover, the design in accordance with the invention is cheaper than the prior design in that its manufacture involves less machining and simpler manufacturing techniques.
The added strength also results from the elimination of the need for a key in a keyway as is used in the prior design involving a separate flange keyed onto a shaft at both the input and output of the pump transmission. The integral flange and shaft design of the pump transmission of the invention makes it possible to manufacture the input and output members out of a one-piece high strength steel forging which is much stronger than the two-part flange and shaft design of the prior pump transmission.
Thus, the design in accordance with the invention is compact, much stronger and involves less machining, and even considering the increased torque carrying ability, the overall size and weight is less. Because of these reductions the ultimate manufacturing cost is much less.
Another advantage of the design in accordance with the invention is that the width between the input flange and the output flange can be reduced by one third as compared with a comparable prior design. The design in accordance with the invention involving integrating the flange and shaft together makes it possible to bring the input and output flanges closer together than in the prior arrangement. This is very critical in applications such as use on a large truck, such as a fire truck, since the shorter this distance the more compact it is possible to make the fire truck i.e., the closer the rear wheels can be to the front wheels.
Another feature of the design in accordance with the invention is that it provides a convenient place for providing a thread for use in actuating a speed counter. The thread is incorporated directly on the shaft portion of the input member which is a convenient and inexpensive location.
Another feature in accordance with the invention is that the input and output flange portions are provided with dual piloting diameters and multiple hole arrangements such that the flange portions can be engaged with a plurality of different standard sizes of truck transmission and rear wheel drive line flanges. Thus, the pump transmission is adapted to be used with a wide variety of trucks and a wide variety of engines that operate at different torques.